Technology & Development Program

United States Department of Agriculture

Forest Service

March 2010

Facilities

• Wood gas produced from biomass is a

renewable energy resource.

• Wood gas was used extensively to fuel

automobile engines and electric

generators during World War II.

• A demonstration biomass gasi�cation

system at the Missoula Technology

and Development Center could

produce nearly 25 kilowatts of

electricity, but it requires an operator

while it is running.

• For a biomass gasi�cation system to

operate most ef�ciently, the heat

generated by the system must be used

as well as the electricity.

7300 1073–2315P–MTDC

For additional information, contact: Scott Groenier project leader; USDA Forest Service, MTDC; 5785 Hwy. 10 West; Missoula, MT 59808–9361. Phone: 406–329–4719 fax: 406–329–3719; email: jgroenier@fs.fed.us

TT he Forest Service is investigating ways to use small-

diameter or low-value trees to produce wood gas for

heating and cooling and to generate electricity. Wood

gas could reduce the consumption of fossil fuels, cut energy

costs, lower the production of greenhouse gasses, and provide

a market for excess biomass.

Biomass gasification—heating biomass to produce

gasses rather than simply burning the biomass—is not a new

technology. When petroleum fell into short supply throughout

Europe, Asia, and Australia during World War II, wood gas

was used to fuel automobile engines and electric generators.

The technology began to lose popularity when natural gas

and petroleum supplies became available after the war. As

the demand for renewable energy resources has increased, so

has interest in biomass gasification.

The Promises and Pitfalls of Using Wood To Produce Electricity

James “Scott” Groenier, Project Leader; Gary Kees, Mechanical Engineer; Ted Etter, Electronics Engineer;

Samantha Lidstrom, Project Assistant; Charles Showers, Program Leader

Despite the potential benefits of biomass gasification,

problems must be solved before biomass gasification

is reliable and economical enough for the small-scale

applications discussed in this tech tip.

2

Equipment TypesGasification is partial combustion of a carbon-rich

material to produce a synthesis gas (syngas), a mixture of

carbon monoxide, hydrogen, carbon dioxide, methane, water

vapor, and nitrogen. Wood gas is one type of syngas. A

carbon-rich biomass and a controlled amount of oxygen are

combined at high temperatures in a gasifier. Updraft gasifiers

introduce oxygen through the base of the gasifier and collect

gas at the top. Downdraft gasifiers introduce oxygen through

the top or sides of the gasifier and collect gas at the bottom.

The updraft gasifier tolerates higher moisture content in

the biomass than the downdraft gasifier, eliminating much of

the need to dry fuel. However, the synthesis gas produced by

the updraft version has more tar oil than is ideal for internal

combustion engines. Fuel for updraft gasifiers is customarily

limited to coal and nonvolatile materials such as charcoal.

In downdraft gasifiers, tar oil is consumed in the

combustion process. Downdraft gasifiers are the ideal choice

for the Forest Service because the gas they produce can be

used in internal combustion engines with little tar buildup.

Biomass FuelSelecting the correct biomass fuel is crucial. Wood

chips must be relatively small and about the same size to

ensure uniform heating of the fuel and to prevent equipment

problems. Irregularly shaped materials may get stuck in the

equipment (figure 1).

Although wood pellets may be a desirable biomass fuel,

they cannot be produced onsite. The BioMax’s computer

must be adjusted when wood pellets are used. Otherwise,

tar accumulates, based on the experience of researchers

at Auburn University (Christian Brodbeck, personal

communication 2010).

Biomass fuel should have a moisture content of 15

percent or less, although most gasifiers will function with

fuels that have a moisture content of up to 25 percent.

Usually, fuel should be dried before it is fed into a gasifier

(figure 2).

According to the Community Power Corporation, which

produces BioMax gasification systems, the characteristics of

good biomass fuels include:

• Available in large quantities over the long term

• Low moisture content

• Dense

• Small, flows well

• Low ash content

• Low cost, not subject to large price swings

• Available locally

• Nontoxic, easily handled

Additional information on biomass fuels is available

in the Community Power Corporation’s frequently asked

questions Web page (http://www.gocpc.com/faq.html).

Figure 1—Wood chips (left) are a desirable fuel for gasification because their shape and size are uniform. Shreddings (right) can cause uneven heating and can jam the equipment.

Figure 2—This grate screens out chips that are too small or too large as fuel is fed into the BioMax system.

3

Operation and MaintenanceTo produce clean, usable synthesis gas, typical

operations follow these guidelines:

• Regulate the temperature of biomass in the gasification

chamber—Char and tar are produced if too little

oxygen is introduced. If too much oxygen is present,

the produced gas will burn. The temperature of the

gasification chamber (figure 3) should be higher than

800 degrees Celsius for efficient carbon conversion

and relatively low tar production. The proper operating

temperature is maintained by controlling the oxygen

ratio in the gasification chamber.

• Ensure that biomass fed into the gasifier is a consistent

size—Irregular-shaped material, such as shreddings,

can cause bridging or channeling. The reduced fuel

flow increases the oxygen-to-fuel ratio and can cause

problems if the synthesis gas begins to burn.

• Use biomass with low ash and low contaminants (such

as silica) to prevent formation of “clinkers” at high

temperatures. These clinkers can disturb air and fuel

flow in the gasifier.

The Community Power Corporation estimates that

the BioMax system requires on average one-half hour of

maintenance a day. A 50-kilowatt BioMax system has

delivered power for 732.6 hours (30.5 days) out of 745.4

hours (31.1 days) for 98.3 percent availability.

Gasi�cation chamberGasi�cation chamber

AirvalvesAir valves

Figure 3—Air valves regulate the temperature inside the BioMax gasification chamber.

Mobile BioMax Operation at MTDCSince 2008, the Missoula Technology and Development

Center (MTDC) has worked with the University of Montana’s

energy technology program to demonstrate the potential

for renewable energy produced by a mobile BioMax system

(figure 4).

A grant by the Biomass Research and Development

Initiative, a joint effort of the U.S. Department of Agriculture

and the U.S. Department of Energy, provided funding to

purchase the BioMax system. The 25-kilowatt system is

completely mobile, but stays at MTDC when it is not on

display elsewhere. The BioMax system’s electric generator

(figure 5) feeds power to MTDC when the system is operating,

offsetting power purchased from NorthWestern Energy.

Figure 4—The mobile BioMax system at MTDC.

Electrical panel for generator

Electrical panel for generator

Electric generatorElectric

generator EngineEngine

Figure 5—The BioMax’s electric generator is driven by a standard V-6 engine modified to run on wood gas.

4

Stationary BioMax Operation at the Southern Research Station

The Southern Research Station has installed a

25-kilowatt BioMax system at the Kisatchie National Forest’s

Winn Ranger District office in Winnfield, LA. The BioMax

system can provide all of the power needed by the Winn

Ranger District. Excess power is returned to the power grid.

Thomas Elder, research chemist for the Southern

Research Station in Pineville, LA, says that the BioMax

system is being used to provide electricity and to study the

feasibility of gasification technology. The BioMax system

was attractive because it can be purchased as a turnkey

system and the Community Power Corporation has been

available for support when problems arise.

Additional information on the Southern Research

Station’s BioMax system is available at:

• http://www.srs.fs.usda.gov/usfr/Gasification_Unit_

Overview_Presentation.pdf (2.98-megabyte Acrobat file)

• http://www.srs.fs.usda.gov/usfr/Gasification_Unit_

Overview_Video.wmv (3-minute 38-second movie)

Mobile BioMax Operation at Auburn University

Christian Brodbeck, a research engineer at Auburn

University, operates a mobile 25-kilowatt BioMax system and

in his opinion, the BioMax system needs the following:

• The heat must be used by a heating system.

• The electricity must be needed onsite or be sold to an

electric company.

• The biomass that fuels the unit must be free or have its

cost subsidized.

Mobile BioMax systems require extra precautions

compared to stationary systems, Brodbeck said. After the

mobile BioMax system has been moved, the system should

be checked to ensure that parts have not vibrated loose.

What Information Is Available?In 1989, the Federal Emergency Management Agency

released the report “Construction of a Simplified Wood Gas

Generator for Fueling Internal Combustion Engines in a

Petroleum Emergency” (http://www.woodgas.net/files

/FEMA%20emergency%20gassifer.pdf). The report includes

instructions for fabricating and implementing a device

modeled closely on the Imbert Gasifier used during World

War II to produce transportation fuels. This device can be

produced using readily accessible materials by anyone with

moderate machining skills.

Forest Service researchers modeled the economic

feasibility of gasifying slash to power electric generators and

return electricity to the grid in southern Oregon (“Fuel to Burn:

Economics of Converting Forest Thinnings to Energy Using

BioMax in Southern Oregon,” http://www.fpl.fs.fed.us

/documnts/fplgtr/fpl_gtr157.pdf). Although the largest BioMax

system commercially available generates just 75 kilowatts of

electricity, researchers considered whether the systems might be

economical if they generated 100 or 1,000 kilowatts. The report

concluded that a biomass gasification plant producing 1,000

kilowatts or more of electricity may be worth considering:

• If the plant could be located at a forest landing near an

existing powerline.

• If the plant received operating subsidies of at least 1.8

cents per kilowatt hour.

The Energy Efficiency and Renewable Energy (EERE)

office of the U.S. Department of Energy published a 2006

report (http://www.nrel.gov/docs/fy06osti/39945.pdf) outlin-

ing improved techniques for purifying gas produced by small

biomass gasification systems. In August 2006, EERE collabo-

rated with Mount Wachusett Community College in Gardner,

MA, to determine the benefits of a modular biomass gasifica-

tion system used to supply electricity, heating, and cooling for

a daycare facility on its campus. The project is ongoing.

Researchers at Mississippi State University and Texas

A&M studied the quality of the gas produced by an 18-kilowatt

gasification system manufactured by the Community Power

Corporation in Littleton, CO. The authors said that “Overall,

the system, which has extensive electronic controls based on

temperatures and pressures at numerous locations, produced

a remarkably consistent high-quality syn-gas [synthesis gas]

regardless of input parameters.” (“Syn-Gas Quality Evaluation

for Biomass Gasification with a Downdraft Gasifier” 2009, http://

asae.frymulti.com/newresults.asp, search for “syn-gas quality”).

5

Where Do We Go From Here?The 25-kilowatt BioMax system (figure 6) being

demonstrated at MTDC is a work in progress.

One of the biggest challenges is fully using the waste

heat the system generates. Now waste heat dries the wood

chips used as fuel. About 50 percent of the biomass energy

is converted to heat—just 20 to 30 percent is converted to

electricity.

The BioMax system requires an operator when it is

running, an expense that the energy being produced cannot

cover. If the system could be operated remotely, and the heat

it produces could be used, the system probably could save

money for MTDC while putting renewable resources to work.

Gasi�cation chamberGasi�cationchamber

ControlpanelsControlpanels

Figure 6—The BioMax system includes a module that heats wood (or other biomass) to produce wood gas.

James “Scott” Groenier began working for MTDC

during 2003 as a civil engineer. Groenier earned a bachelor’s

degree from the University of Wisconsin at Madison and

a master’s degree from Montana State University. He

worked for the Wisconsin and Illinois State Departments

of Transportation before starting his career with the Forest

Service. He worked as the east zone structural engineer for

the Eastern Region and as a civil engineer for the Ashley and

Tongass National Forests.

Gary Kees joined MTDC in 2002 as a project leader. Kees

works in the reforestation and nursery, forest health, and

GPS programs. His current projects involve laser guidance

systems, ATV and backpack sprayers, nursery seeders,

and remote weather stations. Kees, who has a degree in

mechanical engineering from the University of Idaho,

worked for 10 years as a mechanical and structural engineer,

project manager, and engineering group leader for Monsanto

Co., in Soda Springs, ID.

Ted Etter joined MTDC in 2002 as an electronics engineer

and project leader. He has 20 years of experience designing

test equipment, display devices, and medical instrumentation

for private industry. For 6 years before joining MTDC, Etter

taught courses in electronics at the University of Montana

College of Technology, Missoula. His work at MTDC

includes projects in wireless communications, alternative

energy sources, instrumentation, and process control.

Etter received a bachelor’s degree in mathematics from

the University of Oregon and a master’s degree in teacher

education from Eastern Oregon State University.

Samantha Lidstrom is a civil engineering student at

Montana State University in Bozeman, MT. Lidstrom has

worked part time for MTDC as a research and publications

assistant since 2008.

Charles Showers, professional engineer, became

engineering program leader at MTDC in 2002 after serving 2

years as operations program leader. Showers came to MTDC

after 9 years as assistant forest engineer on the Payette

National Forest. He began his Forest Service career on the

Boise National Forest after 8 years as a construction project

engineer with the Idaho Transportation Department.

About the Authors

6

The Forest Service, United States Department of Agriculture (USDA), has developed this information for the guidance of its employees, its contractors, and its cooperating Federal and State agencies and is not responsible for the interpretation or use of this information by anyone except its own employees. The use of trade, firm, or corporation names in this document is for the information and convenience of the reader and does not constitute an endorsement by the Department of any product or service to the exclusion of others that may be suitable.

The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and activities on the basis of race, color, national origin, age, disability, and where applicable, sex, marital status, familial status, parental status, religion, sexual orientation, genetic information, political beliefs, reprisal, or because all or part of an individual’s income is derived from any public assistance program. (Not all prohibited bases apply to all programs.) Persons with disabilities who require alternative means for communication of program information (Braille, large print, audiotape, etc.) should contact USDA’s TARGET Center at (202) 720-2600 (voice and TDD). To file a complaint of discrimination, write to USDA, Director, Office of Civil Rights, 1400 Independence Avenue, S.W., Washington, D.C. 20250-9410, or call (800) 795-3272 (voice) or (202) 720-6382 (TDD). USDA is an equal opportunity provider and employer.

Library Card Groenier, J. Scott; Kees, Gary; Etter, Ted; Lidstrom, Samantha; Showers, Charles. 2010. The promises and pitfalls of

using wood to produce electricity. Tech Tip 1073–2315P–MTDC. Missoula, MT: U.S. Department of Agriculture, Forest

Service, Missoula Technology and Development Center. 6 p.

Biomass gasification is partial combustion of a carbon-rich material to produce a synthesis gas. Synthesis gas is a

renewable energy resource that may reduce the use of fossil fuels, cut energy costs, reduce production of greenhouse gasses,

and provide a market for excess biomass. The Missoula Technology and Development Center has worked with the University

of Montana College of Technology’s energy technology program to demonstrate the promises and pitfalls of using a

25-kilowatt portable downdraft biomass gasification system to produce electricity.

Keywords: alternative energy, biogas, biomass, BioMax, Community Power Corporation, downdraft gasifiers, forest

health, fossil fuels, greenhouse gasses, renewable energy, syngas, updraft gasifiers, wood gas

For additional information about gasification, contact

Scott Groenier at MTDC:

USDA Forest Service

Missoula Technology and Development Center

5785 Hwy. 10 West

Missoula, MT 59808-9361

Phone: 406–329–4719

Fax: 406–329–3719

Email: jgroenier@fs.fed.us

Electronic copies of MTDC’s documents are available on

the Internet at:

http://www.fs.fed.us/eng/t-d.php

Forest Service and Bureau of Land Management

employees can search a more complete collection of

MTDC’s documents, CDs, DVDs, and videos on their

internal computer networks at:

http://fsweb.mtdc.wo.fs.fed.us/search/